1. Field of the Invention
The present invention relates to compositions, e.g., heavy duty detergent compositions, automatic dishwashing liquid detergent compositions or hard surface cleaning compositions containing a detergent surfactant system and further containing both a nitrogen containing compound and one or more specific metal salts. The metal salt and nitrogen containing compound are believed to complex and disassociate in such a way as to create a pH jump system. More specifically, the pH of the composition is maintained at a desired level in product and yet rises upon product dilution. The invention further relates to a method of creating a pH jump system while laundering (i.e., increasing pH of wash solution) by diluting a composition containing said surfactant system, said N-containing compound and said metal salt.
2. Background of the Invention
Liquids which have a lower pH in product form than when they are diluted in wash are desirable for a number of reasons.
First, lower product pH is desirable for providing improved stability for compositions comprising one or more enzymes. That is, high product pH (e.g., pH above 7) is known to denature and destabilize enzymes. In addition, high product pH is known to destabilize peracid bleach compounds. While certain peracid bleaching compounds can be stably incorporated in liquid detergent products at low pH, a pH close to the pKa of the compound (e.g., pH of about 8) is required for optimal bleaching performance. Furthermore, since high pH is desirable for increased detergency in the wash,it is desirable to have a pH "jump" on dilution of a liquid product from a range which is more stabilizing to the enzyme or peracid (i.e., lower pH range) to a range providing greater detergent activity.
Both U.S. Pat. No. 4,959,179 to Aronson et al. and U.S. Pat. No. 5,089,163 to Aronson et al., teach compositions in which a pH jump system is used to stabilize lipase in the presence of a protease and in which the pH increases from product to dilution in the wash. The pH-jump system used in these references is a combination of polyols and borate.
Both U.S. Pat. No. 4,992,194 to Liberati et al. and U.S. Ser. No. 07/860,828 (filed Mar. 31, 1992), assigned to the same assignee as the subject invention, teach a polyol/borate pH jump system for stabilizing peracid compounds. However, it is desirable to find pH systems which do not use borate.
U.S. Pat. No. 4,992,212 to Corring et al. teaches light duty liquid detergent compositions comprising an organic base, such as amines, a zinc salt, and a complexing agent. The compositions of the reference have a pH of 9-11. Since the organic base is already close to or at its buffering pH (i.e., pH of the composition is already above 9), it is clear that no pH "jump" system is contemplated. That is, given this starting pH, there is really no room for a jump to occur. Moreover, the reference is concerned with light duty liquids useful in cleaning dishes and certainly does not teach or suggest a method of creating a pH jump system while laundering (e.g., washing clothes).
U.S. Pat. No. 4,069,066 to Hindle et al., cited as a reference in the parent application of the subject application, discloses a method and composition for cleaning polished surfaces. The composition comprises an amine-derived nitrogenous surfactant, amine impurities introduced into the composition with the surfactant, a salt of a metal ion capable of complexing the amines, and water. The impurities are said to be introduced during formation of the nitrogenous surfactant (column 5,lines 17-19). The amounts of metal salt exemplified are extremely small and appear to be below the amounts contemplated by the subject invention. Moreover, the reference is concerned with cleaning polished surfaces and is certainly not concerned with a method of creating a pH jump system while laundering.
U.S. Pat. No. 4,318,818 to Letton et al. relates to a stabilized aqueous enzyme composition which contain a surfactant system, N-containing compounds and calcium ions. It is said that zinc may replace the calcium. Even if this were so, however, the maximum amount of calcium (i.e., 10 millimoles) corresponds to 0.04% calcium or 0.065% zinc which is below the amount of metal cation used in the invention of the subject application. Moreover, the reference is completely unconcerned with a method of creating a pH jump system while laundering.
U.S. Pat. No. 4,002,571 to Anderie refers to cleaning compositions in which surfactant should be present in minor amounts and desirably be absent altogether.
U.S. Pat. No. 4,117,557 to Postlethwaite is clearly concerned with powder compositions which have nothing to do with pH. The only reference to pH in the reference is to already diluted compositions.
Thus, there is a need in the art for compositions which have an initial pH more stable to enzymes or peracids (i.e., pH of 8 and below). There is further a need in the art to provide a method of creating pH jump systems (for laundering) which are alternative to the borate/polyol system of the art.